RNAs transcribed from the cDNA clones of wild-type or cell culture adapted hepatitis A virus (HAV) or mutants constructed from these clones are being studied to determine the organization of the hepatitis A virus particle. In vitro translation assays are being used to determine gene boundaries. A mutagenesis system was developed to exactly replace entire genes within a cloned DNA. This mutagenesis system was used to construct picornaviral chimeric genomes containing genes from both HAV and poliovirus. Translation of RNAs from these constructs yielded chimeric polyproteins. Processing and assembly properties of these proteins will be studied to determine parameters affecting the structure of the HAV virion and the regions comprising neutralization epitopes.